Quoted from nipper2u:I have a Velodyne sub to a pinsub out board and like it as long as I don't turn it up too much. It does BZZZ when I power up and POP when I shut it down (is fine in-between). Not sure after all this time if that is normal or has anything to do with sub and board, but something worth mentioning. One of several mods I would do again.
If it helps the POP is part of the normal operation for most pinball machines and the subwoofer is probably amplifying it. The POP is very low frequency, so the subwoofer picks it up.
Feel free to send us a sound sample where you have the BZZZ and Mark will listen to it and see if it's anything.
Glad to hear you wold do it again 
~Sandra
Minneapolis, MN
